The major purpose of this study is to explore control of SV40 gene expression, both in lytically-infected and in virus-transformed cells. This involves the location of regions of the SV40 genome involved in control of gene expression, the isolation of sets of mutants with lesions in these regions, and the use of these mutants to probe control of viral gene expression. We are currently engaged in the following specific studies: ) Detailed characterization of six new mutants with deletions between 0.199 and 0.22, all of which are viable for growth in african green monkey kidney cell lines. We are studying their macromolecular synthesis, DNA sequence, transformation properties, and adenovirus helper function. 2) Application of recombinant DNA technology for the isolation of mutants of SV40 DNA in pure form for use in preparing mutants via D-loops and other methods and the use of recombinant DNA technology for the direct isolation of mutants of SV40. 3) Studies are underway to examine the utility of directed single-base mutagenesis in SV40. Fragments of DNA, carrying a single base alteration, are synthesized enzymatically with polynucleotide phosphorylase, annealed to single-stranded circles of SV40 DNA, and elongated enzymatically. From these heteroduplexes, mutants can be isolated. This is being done in collaboration with Dr. Michael Smith, University of British Columbia.